1. Field of the Invention
The present invention relates to fiber optic communication systems. In particular, embodiments of the present invention relate to apparatuses and methods that can be used to detect the presence of high speed data from an active component in a passive optical network.
2. Description of the Related Art
Conventional Optical Fiber Identifiers (OFIs) are rugged, handheld, and easy-to-use fiber optic test instruments designed to detect optical signals transmitted through an optical fiber without disrupting traffic.
One type of optical fiber identifier that can be used to test optical fibers uses the principle of macrobending. A macrobend device is one that imposes a large physical distortion on the fiber, by, for example, causing the fiber to conform to the shape of a bending part. By bending the fiber around a bending part, the macrobend optical fiber identifier can detect light which escapes the fiber at the bend.
Another type of device used to identify optical fibers is a microbend device. A microbend device imposes a small bend on the optical fiber in relation to the physical dimensions of the fiber.
During installation, maintenance, rerouting, or restoration, it is often necessary to isolate a specific fiber. By simply clamping an OFI unit onto a gently bent fiber, the unit will indicate whether the fiber is in use. More specifically, a related art OFI may be able to detect if there is a signal, tone, or traffic present on the fiber and identify the signal direction, if any.
An example of a related art Optical Fiber Identifier can be seen in FIG. 1. The Optical Fiber Identifier 100 of FIG. 1 includes a fiber groove 120, into which the fiber 110 is inserted for signal detection. Additionally, the OFI 100 of FIG. 1 includes a plurality of signal indicators, such as, for example, Traffic indicator 130, No Signal indicator 140, Tone indicator 150 and Power indicator 160.
The No Signal indicator 140 indicates that no light has been detected in the optical fiber. The Traffic indicator 130 indicates that light is present on the fiber, and may also indicate the direction of the light. The Power indicator 160 simply alerts the user if the battery needs to be changed. The Tone indicator 150 may indicate the presence of a tone signal. In the related art, a tone signal can be used to select a fiber from a plurality of fibers. Typically, this involves connecting one end of an unknown fiber to a light source at one location and injecting a predetermined tone signal. Commonly a light source that generates 270 hz, 1 Khz and 2 Khz signals is used as the tone generator. A tone signal is typically a square wave that has a 50% duty cycle, however, other duty cycles may be used. Next, a related art OFI, such as OFI 100, is clamped onto a bundle of unknown fibers at the other location. If the OFI detects the predetermined light signal, for example 2 Khz, the fiber is identified.
With regard to duty-cycles, this can be understood as the percentage of time the signal is above a threshold. For example, the duty cycle of a light signal may be the percentage of time that light is transmitted through the fiber.
Optical fiber identifiers, such as OFI 100, are normally set to have a very large sensitivity but a rather small bandwidth. More specifically, the bandwidth is usually set to be between 0 and 2 Khz. Since these OFIs are designed to detect 2 Khz or less, there is no reason to make the bandwidth any greater than 2 Khz. Moreover, electrical noise in a circuit is directly proportional to the bandwidth, thus, the bandwidth is selected to be no more than that which is necessary. In another approach to increasing sensitivity, related art optical fiber identifiers typically rely on DC-coupling, as AC-coupling may negatively impact signals at low frequencies.
However, new high speed fiber optic communication systems, such as passive optical networks (PONs), are now being deployed to businesses and residential areas around the world. In these new systems, the rates of data transmission are high, for example, greater than 155 Mbps. Because related art OFIs, such as those described above, have a limited amount of bandwidth, these OFIs have only a limited value in the new high speed systems. In particular, because the OFI described above is set to detect only low speed signals, high speed signals are only displayed only as an average of the time light is present on the fiber and the time no light is present. Consequently, the OFI is not able to detect the direction of a signal with the accuracy required.
Consider the situation where one end of the optical fiber under test is connected and the other end is disconnected. In this case the OFI described above may indicate that there is traffic and would give no indication that there is an obvious problem with this disconnected fiber. Because the OFI described above has only a limited bandwidth, and the duty cycle of the new high speed fiber optic systems can be very small, the OFI described above may be able to provide an average power, but cannot accurately detect the upstream PON signals being transmitted through the optical fiber.
Accurately detecting disconnected optical fibers can be essential for a high speed network provider. That is, without an ability to accurately detect and identify disconnected fibers, it is very difficult for the network provider to keep accurate records of who is connected and who is not connected to their network. Much like the phone system, an individual fiber is brought to a box on the side of an individual business/residence. At the business/residence, the fiber may or may not be connected to the network inside the structure, similar to traditional phone and cable TV systems. Now consider the situation where a customer subscribes to this high speed network and then decides to discontinue service. At this time, the provider simply disconnects this fiber at box on the side of the business/house. Now, unless the provider's database is updated, the provider has a lost fiber at the distribution point for this business/residence. In particular, unless the line is physically disconnected at the distribution point and an alarm goes off in the provider's network, the provider has lost a line. Disconnecting lines and checking for alarms is time consuming and can temporarily disrupt service to customers.
Also, optical fibers used in the field typically have diameters of 900 um, 2 mm, and 3 mm. Optical fibers having diameters of 2 mm and 3 mm consist of a 900 um buffered fiber surrounded by a flexible strength member, such as Kevlar®, and enclosed by a polymer tube. The polymer tube stiffness can vary greatly between fibers and over different temperatures.
In view of the above, there is need for an optical fiber identifying device which can accurately detect the presence or absence of a predetermined high speed signal on an optical fiber.